In pleated media filter elements, the performance of the filter will be enhanced or diminished by the ability of the fluid being filtered to pass freely and completely through the media. If open flow paths are maintained between the pleats, the filter normally will operate at its optimum. If, on the other hand, the flow paths through the filter are somehow obstructed or reduced, e.g. when pleats bunch together, the filtering capacity of the media will be diminished. Thus, maintaining a certain spacing between successive pleats in an assembled pleated filter element is extremely important to the overall performance of that element.
Several methods for achieving equal pleat spacing have been devised by others and are known in the art. These include the use of figure eight shaped pleats, the bonding of the pleat tips to the filter liner by using a spiral bead of adhesive and the use of string, paper or adhesive as a spacer between individual pleats. Also, various methods for corrugating or creating bumps and dimples upon the pleat surface have also been employed in attempts to obtain reliable, self-spacing filter element pleats.
There are disadvantages, however, to all of the above prior art methods. The figure eight pleat arrangement relies upon a predetermined pleat density to obtain optimum performance. Although the concept of a figure eight pleat was originally intended to achieve self-spacing pleats, such a result has not been consistently and reliably obtained from this method. Figure eight pleat configurations are difficult to obtain at high pleating rates and the effectiveness of the figure eight pleat is largely negated under conditions of elevated temperature and humidity. The methods of bonding pleat tips to a liner or placing a spacer element between the pleats each require an additional step in the manufacturing process and involve a material "add on" which thus increases the cost of the construction of the filter. Forming dimples or bumps which project outwardly from the surface of the pleat would initially space the pleats apart, however during the process of forming such projections the filter media itself is often damaged thereby reducing the effective area available for filtration.
In U.S. Pat. No. 4,452,619 (of which I am a co-inventor), we invented a mechanism for establishing pleat spacing which was particularly well suited to elements with low pleat density of roughly less than 12 pleats per inch (5 pleats per cm). In that invention, a hollow blade is employed which scores a pattern having an unscored island bounded by semicircular or eliptical score lines. While this system achieves excellent results at low densities, the nature of the scoring blade does not permit its effective use at higher densities.
The present invention discloses a unique pleat spacing tool and method for using same which produces the desirable results obtained for lower densities as explained in U.S. Pat. No. 4,452,619 but allows for much higher density filter packs.
The recurring disadvantages of the prior art are overcome in the present invention in that the method of practicing the invention requires a minimum of manufacturing steps and there is no need for additional structural components to achieve reliable and dependable spacing between the pleats contained in the filter element.